As one of the most high-profile and feared loyalist terrorists of the Troubles, the killing of Johnny Adair would have been a "huge scalp for dissident republican groups".

That was how 'Mad Dog' Adair's former sidekick and fellow target Sam 'Skelly' McCrory described the Scottish murder plot during the trial of three men in Glasgow earlier this year.

Both loyalists had fled across the Irish Sea a decade ago after Adair tried to take control of the UDA when he was released from prison as part of the Good Friday Agreement.

The fallout led to a deadly internal UDA feud and the pair were forced from their old Shankill Road stronghold in west Belfast.

Adair eventually settled in the port town of Troon with a new girlfriend, while ex-gunman McCrory, who is openly gay, ended up in Ayrshire.

Anton Duffy (39), Martin Hughes (36) and Paul Sands (32) were arrested in 2013 after two major Police Scotland investigations into terrorism and organised crime.

Duffy, from Donegal, was the ringleader of an unaffiliated active service unit inspired by dissident republicanism and planned to carry out the double murder with Sands and Hughes while on home leave from prison, according to police.

Duffy was passionate about a united Ireland and believed Gerry Adams and Martin McGuinness were "traitors" who had sold out the republican cause by agreeing to the Agreement in 1998.

He wanted to shoot McCrory dead first using a pistol and then quickly target Adair using an AK-47 assault rifle he called "the big fella".

Every few weeks while on home leave back to his flat in Old Castle Road, Glasgow, Duffy sprang into action, meeting, phoning and texting criminal associates in a bid to get his hands on weapons.

Duffy even approached Celtic star Anthony Stokes in a bar, asking him to get his father to pass a message on to someone in Ireland to obtain weapons.

Regulars reacted with fury and Duffy was thrown out of the pub and seen jumping up and down with rage by undercover police. In one bugged conversation he was heard boasting to girlfriend Stacey McAllister: "I'm trying to get a war started and get as many guns and explosives as I can."

Operation Hairsplitter was set up late in September 2012 to investigate an attempt to procure firearms, including the AK-47, by the gang led by Duffy.

It was feared that if the murders had been carried out there would have been huge ramifications on both sides of the Irish Sea.

But the would-be killers didn't know MI5 had got wind of their plans and had authorised the bugging of Duffy's flat. Hughes' car also had a bug placed in it and undercover police followed them.